The present invention relates to novel thermosetting resin composites suitable for making high performance structures and processes related thereto.
There are a number of thermoset resins which are known to have what are called "high performance" properties; i.e. they have high heat resistance, high modulus, and high compression, tensile, and interlaminar shear strength, but relatively low resistance to impact. These thermosets are being used or considered for use in various aerospace, automotive and industrial products where high modulus, high strength and high heat resistance is necessary. These high performance thermoset resins include epoxy, bismaleimide, cyanate ester, and bisoxazoline-phenolic copolymer types.
There is particular need in the aircraft industry (aerospace, military, and commercial) for lightweight, high performance materials to be used for making structural elements. For proposed future aircraft, such as the advanced civil transport (subsonic) and the high speed civil transport which is proposed to fly at supersonic speeds, the structural elements thereof, such as the body and wing frame, ribs, spars, stringers, skins, and the like, must operate under such conditions that plastic composites used to make the same must withstand temperatures up 175.degree. C. to to 200.degree. C. while maintaining a high modulus (stiffness), high compressive and shear strengths, resistance to heat distortion, low coefficient of thermal expansion, and having excellent thermal shock resistance. In addition such plastics must have excellent adherence to reinforcing materials, whether they be carbon fibers or carbon woven fabrics, glass fibers or glass woven fibers, and, in some applications, adhere strongly to metals such as aluminum, iron, and copper. However, the above noted high performance thermoset resins are lacking in adequate toughness/resistance to impact and crack growth and require addition of "tougheners" for practical use in aircraft.
It has been known to "toughen" such resins in order to increase their resistance to impact damage and crack growth to which they are exposed in aerospace and other aircraft uses where structural elements made therefrom are exposed to high temperatures, impact, and/or high physical stress. However, materials such as acryonitrile-butadiene elastomers, and the like, which have been added to such high performance polymers to toughen the same have not been found to be suitable for thermosets intended for high temperature use. In such cases while toughening the resin they also act to lower the heat distortion temperature of the overall structures formed from such composite resin. The presence of reinforcing carbon and glass fibers still does not give the necessary toughness properties.
For high temperature structural uses it is necessary to achieve the toughening enhancement without substantially reducing the glass transition temperature or heat distortion temperature of the resultant toughened composite.